Objective: To evaluate the effects of four herbal medicine extracts on a rat model of inflammatory hyperalgesia.
Design/interventions: Inflammation was induced by injecting complete Freund's adjuvant (CFA) into one hindpaw of each rat. Four herbs that are routinely prescribed in Traditional Chinese Medicine for treatment of pain were used: Duhuo (Radix Angelicae Pubescentis), Bai jiang cao (Patriniae Herba cum Radice), Yan hu suo (Rhizoma Corydalis) and Sanqui (Panax Notoginseng). The crude water extracts of the herbs were inected intraperitoneally following a repeated treatment profile.
Outcome measures: Thermal hyperalgesia was assessed by testing each rat's paw withdrawal response to a noxious thermal stimulus. The magnitude of edema was determined by measuring the maximal thickness of the paw with a caliper. The effect of herb extracts on motor performance was assessed by using an accelerating rotarod test.
Result: Duhuo, Bai jiang cao, and Yan hu suo significantly attenuated CFA-induced hyperalgesia at 2 hours and facilitated the recovery from hyperalgesia (p < 0.05), when compared to saline-treated rats. The CFA-induced edema was reduced by Duhuo at 24 hours, 72 hours and 168 hours; Bai jiang cao at 24 hours, and Yan hu suo at 24 hours and 168 hours. Sanqi did not produce any significant effect on inflammation and hyperalgesia. The rotarod performance was slightly reduced by Bai jiang cao, Yan hu suo, and Sanqi (p < 0.05) but not by Duhuo treatment.
Conclusion: The present study identified Duhuo as a selective and effective herbal agent in attenuating persistent hindpaw inflammation and hyperalgesia in rats. These results indicate that some herbal agents may provide an alternative approach to the treatment of persistant inflammatory pain and hyperalgesia.